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Abstract:

A vehicle includes at least one cooling circuit for cooling a fuel cell
system. The cooling circuit includes at least one cooling heat exchanger,
a cooling medium transportation device and a heat exchanger in a fuel
cell stack of fuel cell system. Cooling heat exchanger is affected by
motion-related air flow as cooling air. The cooling heat exchanger is
constructed in at least two stages, which are arranged in such a way that
they are serially flowed through, one after another, by motion-related
airflow.

Claims:

1-13. (canceled)

14. A vehicle with at least one cooling circuit for cooling of a fuel
cell system, wherein the cooling circuit comprises: a cooling heat
exchanger that includes a first stage and a second stage arranged in such
a way that the first and second stages are flowed through serially, one
after another by motion-related airflow; a cooling medium transportation
device; and a heat exchanger in a fuel cell stack of the fuel cell
system.

15. The vehicle according to claim 14, wherein the first and second
stages of the cooling heat exchanger are flowed through serially, one
after another, by a cooling medium flowing in cooling circuit, wherein
the second stage is flowed through last by motion-related airflow and
first by the cooling medium.

16. The vehicle according to claim 14, wherein the cooling circuit is a
high-temperature cooling circuit exclusively dedicated to cool the fuel
cell stack.

17. The vehicle according to claim 14, wherein the cooling circuit
includes a first section as high-temperature cooling circuit for cooling
the fuel cell stack, a second section, which is parallel to the cooling
heat exchanger, is constructed as low-temperature cooling circuit for
cooling of electrical or electronic components, a low-temperature cooling
heat exchanger is arranged in the cooling circuit parallel to the first
and second stages of the cooling heat exchanger and is located in such a
way that the low-temperature cooling heat exchanger is flowed through by
the motion-related airflow serially in relation to the first and second
stages of the cooling heat exchanger.

18. The vehicle according to claim 17, wherein the low-temperature
cooling heat exchanger is arranged in such a way that it is flowed
through by the motion-related airflow serially before the first and
second stages of the cooling heat exchanger.

19. The vehicle according to claim 17, wherein the first and second
stages of the cooling heat exchanger and of the low-temperature cooling
heat exchanger are arranged in a front area of the vehicle.

20. The vehicle according to claim 17, wherein in an area of the first
and second stages of the cooling heat exchanger and of the
low-temperature cooling heat exchanger a fan is provided in order to
strengthen the through-flow with cooling air.

21. The vehicle according to claim 17, wherein the first and second
stages of the cooling heat exchanger and of the low-temperature cooling
heat exchanger are arranged in a same surface affected by the
motion-related airflow and are arranged as a stack behind one another.

22. The vehicle according to claim 14, wherein the fuel cell stack is
constructed as a stack of PEM fuel cells.

23. The vehicle according to claim 14, further comprising: a climate
control device that includes at least one climate control cooling heat
exchanger in order to cool a climate control medium used in the climate
control device, wherein the climate control cooling heat exchanger is
separate from the cooling circuit for fuel cell system.

24. The vehicle according to claim 23, wherein the at least one climate
control heat exchanger is located in or in front of one wheel arch of the
vehicle.

25. The vehicle according to claim 24, wherein air flow to the at least
one climate control cooling heat exchanger is implemented by the wheel
arches of the vehicle or by side air inlets in a lower area of the
vehicle front, while air is vented through openings in a mudguard in an
area of wheel arch.

26. The vehicle according to claim 25, wherein an area of air intake is
located at a lower height over road surface than the openings for air
venting.

Description:

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] The invention relates to a vehicle with at least one cooling
circuit for cooling a fuel cell system.

[0002] A fuel cell system for a vehicle is disclosed in German Patent
Document DE 196 29 084 C2. The fuel cell system includes a primary
cooling heat exchanger, which, analogously to vehicles with internal
combustion engines, is arranged in such a way that the dynamic pressure
of the motion-related airflow ensures throughflow of ambient air as
cooling air. In order to make use of the dynamic pressure, basically only
the front surfaces of the vehicle can be used for the cooling heat
exchangers. This involves corresponding limitations and disadvantages,
which are described in the following paragraphs, together with other
problems.

[0003] The heat dissipation during operation of fuel cell drive systems in
the case of PEM fuel cell applications represents a problem that places a
limitation on performance, as the greater part of the waste heat that is
generated has to be dissipated into the environment via the cooling
circuit where there are only small differences in temperature. In system
designs that are suitable for use in practice, as a rough starting point
it can be assumed that around the same level of waste heat has to be
dissipated via the cooling circuit as electrical power is generated in
the fuel cell.

[0004] Heat dissipation of the cooling circuit can in principle be
improved by enlarging the cooling surface, improving the throughflow of
the cooling heat exchanger or by raising the temperature of the cooling
medium. Cooling concepts developed to date according to the general state
of technology make use of one or several of these aspects, but are
associated with the disadvantages or restrictions described below.

[0005] The maximum operating temperatures of the PEM fuel cell stacks of
today lies at around 80-90° C. Efforts to increase the temperature
affect the durability (lifetime) of the fuel cell and from today's point
of view can be considered as a long-term target. In addition, water-based
cooling circuits only permit very limited further increases in
temperature, while cooling media capable of functioning at high
temperature (e.g., thermo-oils) have higher sealing requirements,
increased costs and more complex handling. The raising of the front
surface of the cooling heat exchanger, and only in this situation does
the effect described in the aforementioned DE 196 29 084 C2 with regard
to the dynamic pressure occurs subject to severe limitations in
automotive engineering. The main limiting factors are package and design
specifications, and also the desire to achieve the lowest-possible air
resistance factor (cw.A-Wert) in the interests of low vehicle energy
consumption. Improvement of cooling effects using high-performance fans
also brings serious disadvantages. The necessary drive power for the fans
leads to a considerable increase in parasitic losses. This means that the
efficiency rating of the system is reduced. In addition, vehicle
acoustics suffer negative impact.

[0006] For these reasons, the heat dissipation capability of the cooling
circuit presents a limiting factor for the electric performance of mobile
fuel cell systems in vehicles. In order to provide a solution to these
problems in the fuel cell systems in vehicles, German Patent Document DE
10 2005 021 413 A1 discloses the use of additional surfaces in the area
of the vehicle as a cooling surface. However, the design of the vehicle
is then changed accordingly, which is often not desired.

[0007] Furthermore, a cooling circuit for a fuel cell vehicle is described
in U.S. Pat. No. 6,370,903 B1, which uses a high-temperature cooling
circuit with a cooling heat exchanger utilizing the motion-related
airflow for cooling of the fuel cell itself. In addition, for cooling of
the drive motor and of the electrical and electronic components of the
vehicle, a low-temperature cooling circuit is shown in a known form that
is also cooled by a cooling heat exchanger utilizing the motion-related
airflow.

[0008] Vehicles are currently equipped with a climate control device
which, according to the embodiment described here, can be used for
climate control of an interior of a vehicle and for support of the
cooling circuit of the fuel cell. The installation is shown as a heat
pump.

[0009] Basically it is the case that a climate control system also has to
be provided with a climate control cooling heat exchanger in order to
cool or condense the climate control medium used in the climate control
system. The installation is of such a type that very often this climate
control cooling heat exchanger is integrated into the cooling circuit of
the fuel cell, or, as described in U.S. Pat. No. 6,370,903 B1, is
integrated into the low-temperature cooling circuit for the electronic
components.

[0010] In such integration, in the case of use of the climate control
equipment for cooling the interior of the vehicle, the disadvantage
always occurs that the amount of heat entering the cooling circuit is
further increased so that, in particular in the presence of very high
ambient temperatures, the cooling of the fuel cell stack is worsened
further. Because of this worsening of the cooling of the fuel cell stack,
the performance capability of the vehicle equipped with the fuel cell
system is correspondingly reduced. The supporting cooling of the fuel
cell cooling circuit mentioned in U.S. Pat. No. 6,370,903 B1 by means of
an evaporator of the climate control device, exhibits the disadvantage
that such cooling is associated with a comparatively high use of energy
in the climate control device, so that the overall efficiency rating of a
vehicle thus equipped suffers.

[0011] Exemplary embodiments of the present invention provide a vehicle
with at least one cooling circuit for cooling of a fuel cell system that
enables a maximum cooling performance with the minimum energy
requirement, and therefore allows high performance capability of the fuel
cell system, even in the case of difficult ambient conditions.

[0012] Because the cooling heat exchanger in the vehicle according to the
invention is designed with at least two stages, the surface available for
cooling in the cooling heat exchanger is considerably increased. The
arrangement of the at least two stages of the cooling heat exchanger so
that they are blown through by the motion-related airflow as cooling air
serially, one after another, means that the at least two stages can be
used without the necessary flow surface having to be greater. The
installation can therefore be integrated into existing vehicle concepts
without problem, as only the thickness of the entire cooling heat
exchanger or the stack of the stages of the cooling heat exchanger in the
direction of driving is increased because of the higher number of stages,
without the need for a greater flow surface.

[0013] According to one embodiment of the vehicle according to the
invention, the at least two stages of the cooling heat exchanger are
flowed through by a cooling medium flowing in the cooling circuit
serially, one after another, whereby the stage last flowed through by the
motion-related airflow is flowed through first by the cooling medium. As
the individual stages of the cooling heat exchanger are arranged one
behind the other in the direction of travel, these are also flowed
through after one another by the motion-related airflow as cooling air.
This means that in the individual stages there is a different temperature
differential between the cooling medium to be cooled in the respective
stage and the motion-related airflow as cooling air which cools this
cooling medium. Correspondingly, the individual stages of the cooling
heat exchanger can be cooled to different levels. Because the individual
stages are arranged in such a way that they are flowed through serially
by the cooling medium, it can now be achieved that the stage of the
cooling heat exchanger that is flowed though by the warmest cooling
medium is already cooled by the warmest motion-related airflow, in other
words the motion-related airflow that has already been heated by the
other stage. This means that the cooling of the cooling medium is
implemented in the best possible way, as the cooling medium that is still
very warm is cooled by comparatively warm motion-related airflow, so that
there is a sufficient difference in temperature in order to achieve at
least preliminary cooling of the cooling medium in the first stage (from
the point of view of the cooling medium) and in the last stage (from the
point of view of the motion-related airflow). In the one or the
subsequent stages, the cooling medium then will be progressively colder,
in the same way as the motion-related airflow, so that a complete cooling
of the cooling medium to the temperature level which is needed for the
full performance capability of the fuel cell system can be attained.

[0014] In an advantageous further development of the vehicle according to
the invention, the cooling circuit includes a first section as
high-temperature cooling circuit for cooling of the fuel cell stack,
whereby in parallel to the cooling heat exchanger a second section is
designed as a low-temperature circuit for cooling of electrical and/or
electronic components, whereby a low-temperature cooling heat exchanger
is provided and located in the cooling circuit parallel to the at least
two-stage cooling heat exchanger in such a way that the low-temperature
cooling heat exchanger is flowed through by the motion-related airflow
serially to the at least two stages of the cooling heat exchanger.
According to this particularly advantageous further development of the
vehicle according to the invention, a low-temperature cooling heat
exchanger in the form of a further stage from the point of view of the
motion-related airflow is arranged serially to the at least two stages of
the cooling heat exchanger. Accordingly, the installation facilitates
integration of the low-temperature cooling circuit that is already known
and generally used according to the state of technology in fuel cell
driven vehicles for cooling of electrical and/or electronic components
such as for example, the drive motor and the power electronic components,
into the actual cooling circuit. The low-temperature cooling circuit is
then designed as a second section of the cooling circuit, so that
additional tube elements and also possibly an additional cooling medium
transportation device are not required.

[0015] According to one of the possible embodiments of the vehicle, the
vehicle also includes a climate control device. In the embodiment
according to the invention, it is now particularly advantageous if the
climate control device includes at least one climate control heat
exchanger, in order to cool the climate control medium used in the
climate control device, whereby the climate control heat exchanger is
designed so as to be independent of the cooling circuit for the fuel cell
system. This independence of the climate control cooling heat exchanger
for cooling or condensing of the climate control medium of the climate
control device from the cooling circuit of the fuel cell system, ensures
that no additional heat is taken into the cooling circuit for the fuel
cell system via the cooling of the climate control medium. It is rather
the case that this heat, which occurs particularly in the presence of
high ambient temperatures when cooling of the fuel cell system is in any
case difficult, is cooled down elsewhere, so that this additional heat
does not exercise a negative influence on the fuel cell system or its
cooling.

[0016] This means that the fuel cell system can be cooled independently of
the climate control device and can retain its performance capability.

[0017] In a particularly favorable further development of this, the at
least one climate control heat exchanger is arranged in or in front of a
wheel arch of the vehicle. This arrangement in the wheel arches of the
vehicles can be completely independent of the cooling surface of the at
least two-stage cooling heat exchanger of the cooling circuit for the
fuel cell system, without removing any of the surface available to it
over which a dynamic pressure of the motion-related airflow flows. In
addition, the arrangement in or in front of the wheel arches to a large
extent excludes negative influence on the appearance of the vehicle, so
that attention is not drawn to these additional climate control cooling
heat exchangers or only minimal attention is drawn to them.

[0018] Further advantageous embodiments of the invention can be found in
the remaining dependent claims and become clear from the example of the
embodiment which is explained in more detail below with reference to the
drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0019] The drawings are as follows:

[0020] FIG. 1 a schematic view of a vehicle according to the invention;
and

[0021] FIG. 2 a cooling circuit of the vehicle according to the invention
in a preferred embodiment.

DETAILED DESCRIPTION

[0022] In the representation in FIG. 1, a vehicle 1 is shown in exemplary
form comprising a fuel cell system 2, through which electrical drive
power is provided for vehicle 1. Vehicle 1 is driven by a corresponding
electronic system 3 and an electrical drive in the form of an electric
machine 4, which in particular can also be used as a motor or, in a
fashion already known, as a generator during vehicle braking. Fuel cell
system 2 also includes at least one cooling circuit, which is indicated
by tubes 5. A part of cooling circuit 5 is a cooling heat exchanger 6
arranged in the front area of vehicle 1, in other words in the direction
of travel A at the front. In a known manner, a corresponding dynamic
pressure occurs in the front area of vehicle 1, which flows through
cooling heat exchanger 6 as motion-related airflow F and cools the
cooling medium circulating in cooling circuit 5, typically an anti-freeze
substance mixed with water.

[0023] Vehicle 1 in the representation in FIG. 1 should also be provided
with a climate control device 7, which in known fashion is designed for
climate control of the interior space of vehicle 1. For cooling or
condensation of the climate control medium used in climate control device
7, climate control device 7 requires at least one climate control cooling
heat exchanger 8, which here is present independently of the cooling heat
exchanger 6 of the fuel cell system 2 or cooling circuit 5 of fuel cell
system 2. This climate control cooling heat exchanger 8 is arranged as a
wheel arch heat exchanger is or in front of at least one of the wheel
arches 9 of vehicle 1. The term wheel arch heat exchanger refers to a
heat exchanger located between the front bumper and front wheel arch
cover or in the interior of wheel arch 9 or the mudguard, and which is by
the air flowing there because of the forward movement of vehicle 1. The
advantage of such a wheel arch heat exchanger lies in the fact that it
can be located in an area of vehicle 1 without being visible to the
outside in the design of the vehicle.

[0024] In order now to achieve the best-possible throughflow of this
climate control cooling heat exchanger 8 as wheel arch heat exchanger and
in particular in the case that the vehicle is stationary, so as not to
experience circulated of the warmed air in the interior of wheel arch 9,
the climate control cooling heat exchanger 8 can be affected by the
airflow in the wheel arch and the cooling air that is flowing away is
dissipated, for example by corresponding openings in the mudguard, which
are not shown here but which are already known. Additionally, the
inflowing air streams into climate control cooling heat exchanger 8 at a
lesser height above road surface 10, than the height at which it flows
out through the opening in the mudguard. This achieves a flue effect, so
that the warm air flowing off upwards exercises a drawing effect on the
climate control heat exchanger 8 and sucks in fresh air through wheel
arch 9, which can correspondingly cool climate control cooling heat
exchanger 8. This effect occurs independently of the motion-related
airflow, so that a certain cooling effect can be achieved even if vehicle
1 is stationary, without the need for corresponding fans or similar, in
order to achieved forced convection.

[0025] In the representation in FIG. 2, cooling circuit 5 can again be
seen great detail. Cooling circuit 5 consists of a first section 5a, the
so-called high-temperature cooling circuit, which serves for cooling of a
fuel cell stack 11 of fuel cell system 2. This fuel cell stack 11 can in
particular be in the form of a stack of PEM fuel cells, which, as
so-called low-temperature fuel cells, currently represent the
most-widely-used fuel cells used in vehicle applications. A cooling
medium flows into this first section 5a of cooling circuit 5, for example
the water and anti-freeze mixture already mentioned, which is transported
in the first section 5a of cooling circuit 5 by means of a cooling medium
transportation device 12, which for example can be driven by an electric
motor 13. In the area of fuel cell stack 11 itself, a valve device 14 can
be provided, which correspondingly regulates the throughflow through fuel
cell stack 11. In addition, cooling circuit 5 can include further
elements, such as for example a filter 15 and a compensation tank 16,
which are shown here in exemplary form. The cooling medium warmed in fuel
cell stack 11 now flows via cooling medium transportation device 12 to a
first stage 6a of cooling heat exchanger 6 which is correspondingly
flowed through by motion-related airflow F, in order to cool the cooling
medium. After this it reaches a second stage 6b of the cooling heat
exchanger serially downstream in the direction in the cooling medium,
which is also flowed-through by motion-related airflow F, so that in
second stage 6b of cooling heat exchanger 6 the cooling medium is cooled
further. The cooling medium then returns into fuel cell stack 11 via a
3-way valve 17 and via filter 15. The 3-way valve 17 is known for use in
such high-temperature cooling circuits 5a in fuel cell systems 2 and in
particular serves, during the start phase of fuel cell stack 11, to pump
the cooling medium in the circuit only through fuel cell stack 11 and
possibly other components to be cooled 18, indicated here as optional,
without cooling these correspondingly in cooling heat exchanger 6, so
that fuel cell stack 11 heats up relatively rapidly and achieves its
operating temperature quickly.

[0026] Cooling circuit 5 in the representation of FIG. 2 also includes a
second section 5b, which is designed as a low-temperature cooling circuit
and in particular cools the vehicle drive with its motor 4 and the
corresponding power electronic components 3 of fuel cell system 5. Also
in the operation of the elements of the vehicle drive and the power
electronics which are here flowed-through in parallel, corresponding
valve devices 19 are provided, which enable the throughflow to be set
accordingly. Instead of an independent low-temperature cooling circuit,
as is often exhibited in the state of the art, here the second section 5b
which is used as low-temperature cooling circuit, is integrated into
cooling circuit 5 for fuel cell system 2. This second section 5b exhibits
an independent low-temperature cooling heat exchanger 20 and can make use
of an independent optional cooling medium transportation device 21, in so
far as this is necessary. Optional cooling medium transportation device
21 should in any case lie at a lower geodetic height than compensation
tank 16. This second partial section 5b of cooling circuit 5 functions in
such a way that the cooling medium contained in it flows over
low-temperature heat exchanger 20 after flowing through the elements of
the drive or the electrical machine 4 and the electronic components 3 to
be cooled and then is mixed with the cooling medium in section 5a of the
cooling circuit. The partial flow required for section 5b is then again
taken from cooling circuit 5 before reaching 3-way valve 17, in order
also to be able to guarantee corresponding cooling of the electrical or
electronic components 3, 4 in the warm-up phase of fuel cell stacks 11.
Depending on the arrangement of cooling medium transportation device 12
in cooling circuit 5, it may be possible to omit the optional cooling
medium transportation device 21. Both the low-temperature cooling heat
exchanger 20 and stage 6b of cooling heat exchanger 6 are linked with
compensation tank 16 via venting lines.

[0027] Low-temperature cooling heat exchanger 20 and the two stages 6a, 6b
of cooling heat exchanger 6 described here are arranged serially behind
one another in the direction of the motion-related airflow F that is
flowing through them, so that they are flowed through serially one after
the other by cooling motion-related airflow F. This means that the
surface of the cooling heat exchanger in the front area of vehicle 1 is
only required once for all three cooling heat exchangers together, in
order to ensure throughflow of cooling heat exchangers 20, 6.
Motion-related airflow F first flows through low-temperature cooling heat
exchanger 20 and is slightly warmed in this process. This slightly warmed
motion-related airflow F then flows through second stage 6b of cooling
heat exchanger 6 and cools the cooling medium that was already pre-cooled
in stage 6a of first section 5a of cooling circuits 5 down to the
required temperature. After this, motion-related airflow F, which has in
the meantime been considerably warmed, enters first stage 6a of cooling
heat exchanger 6 and here undertakes a type of "pre-cooling" of the
cooling medium in first section 5a of cooling circuit 5. By means of this
design, very efficient cooling of the fuel cell system with all its
components can be achieved with a minimum requirement for surface area in
the front of vehicle 1. Based on the two linked stages 6a, 6b of cooling
heat exchanger 6 and low-temperature cooling heat exchanger 20,
throughflow of this stack at cooling heat exchangers 6, 20 may be
restricted. At least in certain situations or in the case of high outside
temperatures around vehicle 1 it can be useful and helpful to
correspondingly strengthen throughput by motion-related airflow F by
means of a fan 22 and by these means to achieve forced convection of the
cooling air in the stack of cooling heat exchangers 6, 20. This design
with fan 22, which in particular can be operated or not depending as a
result of temperature-related control, is also known from many vehicles
with conventional internal combustion engines and is in common use for
cooling of cooling heat exchangers in vehicles.

[0028] The installation of cooling circuit 5 for fuel cell system 2 is
designed completely independently of climate control device 7 of vehicle
1, which can also be seen in the representation of FIG. 2. This basically
consists of an expansion valve 23, and an evaporator 24 for cooling of
the interior space of vehicle 1, which is here illustrated by the heat
flow with the arrow designated as B. In addition, climate control device
7 exhibits a so-called internal heat exchanger 25, which is known and in
common use for raising of efficiency in climate control devices 7. In
addition, a compressor 26 can be included, which, in the embodiment
described here, feeds the climate-control medium of climate control
device 7 to two climate control cooling heat exchangers 8, in which the
medium is cooled and/or condensed. As already mentioned in the
description of FIG. 1, these climate control heat exchangers 8 are
designed to be independent of cooling circuit 5 of fuel cell system 2 and
can in particular be located in the wheel arches 9 of vehicle 1. In the
representation shown in FIG. 2, two of the climate control cooling heat
exchangers 8 can be seen, which can, for example, be arranged in the
right and left front wheel arches 9 of vehicle 1.

[0029] The installation shown in the representation in FIG. 2 now has, as
already mentioned, the particular advantage that it can be implemented
with the surface flowed against for cooling heat exchangers 20, 6 which
is typically available based on the design of vehicle 1 in the front area
of the installation. Because of the stack of the low-temperature cooling
heat exchanger 20 and the individual stages of cooling heat exchanger 6,
the best-possible cooling of the cooling medium can be achieved in
cooling circuit 5 with the surface available, and with it the
best-possible cooling of fuel cell stack 11. This means that high
performance capacity of fuel cell stack 11 can be achieved, without its
performance being limited because of inadequate cooling.

[0030] This very compact and efficient structure of cooling circuit 5 in
FIG. 2 ensures the best-possible cooling in a vehicle 1 with a fuel cell
system 2. However, use of cooling heat exchanger 6 divided into two or
even more than two stages could also be implemented, if appropriate, in
the form of a cooling circuit 5 in which, analogous to the state of the
art, a low-temperature cooling circuit for electrical or electronic
components 3, 4 is provided independently from the high-temperature
cooling circuit for fuel cell 11 and also, if appropriate, for further
components cooled in it.

[0031] The foregoing disclosure has been set forth merely to illustrate
the invention and is not intended to be limiting. Since modifications of
the disclosed embodiments incorporating the spirit and substance of the
invention may occur to persons skilled in the art, the invention should
be construed to include everything within the scope of the appended
claims and equivalents thereof.

Patent applications by Ralf Hoess, Stuttgart DE

Patent applications by Daimler AG

Patent applications in class With means to guide and/or control air for power plant cooling

Patent applications in all subclasses With means to guide and/or control air for power plant cooling